1. Field of the Invention
The invention relates generally to compositions and methods for forming coatings of selected color on a substrate and more particularly varying the components in aqueous suspensions of organometallic compositions and depositing the suspensions onto a glass substrate to pyrolytically produce a stable coating film of selected color or colors on the glass substrate.
2. Description of the Currently Available Technology
In various industrial applications, it is desirable to form a coating on glass surfaces. For example, automotive windshields have coated areas known as xe2x80x9cshade bandsxe2x80x9d or xe2x80x9cfade zonesxe2x80x9d. In many passenger vans, the back seat and rear windows are coated with a uniformly thick coating. These coated areas reduce visible, infrared or ultraviolet light transmittance to reduce glare, the visibility of the contents of the vehicle and/or decrease solar energy transmittance to reduce heat gain in the interior of the vehicle.
One method for forming coatings on a glass substrate is by the pyrolytic deposition of metal oxide films. In U.S. Pat. No. 3,660,061 to Donley et al., the disclosure of which is herein incorporated by reference, organometallic salts, such as acetylacetonates, are dissolved in an organic solution and are sprayed onto a hot glass surface to form a metal oxide film. In U.S. Pat. No. 4,719,127 to Greenberg, the disclosure of which is incorporated by reference, aqueous suspensions of organometallic salts are sprayed onto a hot glass surface to pyrolytically form metal oxide coatings on the surface.
The presently available coating technology is used to form gray or dark gray coatings, particularly in the automotive industry, so that the coated glass can be used with the widest number of automobile body colors without xe2x80x9cclashingxe2x80x9d with the automobile body color. Additionally, many of the known coated substrates change color or shade upon subsequent heating during tempering and shaping of the coated substrate. This heat induced color shift makes it difficult to produce coated materials of consistent color stability. Further, many of the known coated substrates are not chemically durable e.g. when contacted with solutions having citric acid.
As can be appreciated, it would be advantageous to provide compositions and methods for applying coating(s) of selected transmitted color onto the surface of a substrate which reduce or eliminate the limitations associated with presently known compositions and methods.
This invention related to a method for forming a coating, e.g., a copper and manganese containing coating, of a desired color on a substrate, e.g., a glass substrate by applying a copper containing component and a manganese containing component onto the substrate in a selected ratio to form the coating having the selected ratio of copper to manganese. More particularly, when the ratio of copper containing component and the manganese containing component is one, the coating is blue in transmission. When the ratio of the copper containing component and the manganese containing component is less than about one, the color varies from gray blue to amber in transmission as the ratio decreases. When the ratio of the copper containing component and the manganese containing component is greater than about one, the color varies from gray blue to brown in transmission as the ratio increases.
The invention further relates to compositions for forming coatings of a selected color on a substrate. Copper and manganese containing coatings may be used to form coatings ranging from amber to blue to light brown depending upon the copper to manganese ratio. A chromium, copper and manganese system provides a neutral gray colored coating in transmittance. Cobalt may be added to this copper and manganese system to increase chemical durability e.g. the citric acid durability of the coating. An iron oxide system provides a golden colored coating in transmittance. Copper may be added to this iron oxide system to provide a light grayish-brown colored coating in transmittance. Chromium may be added to the copper iron oxide system to provide a darker grayish-brown colored coating in transmission. A manganic oxide (Mn2O3) coating provides a mauve/lavender colored coating while a film having an (Mn++) (Mn+++)2O4 phase provides a light amber colored film. (Mn++) (Mn+++)2O4 will be referred to as xe2x80x9cMn3O4xe2x80x9d.
The invention still further relates to a method of preventing color shifting of a multi-component or multi-layer coated substrate upon subsequent heat treatment includes the steps of determining the most mobile species in a layer of the coating and placing a concentration gradient layer of an oxide of that mobile species between the substrate, e.g., a glass sheet, and the coating. The concentration gradient layer is preferably applied directly on the glass substrate but may also be applied on a coating layer formed on the glass substrate. Upon subsequent heat treatment, the mobile species in the concentration gradient layer diffuses into the substrate more readily than the mobile species in the coating, which minimizes depletion of the mobile species from the coating and reduces or eliminates an increase in transmittance.